Study For Impact Of Tropospheric Ozone Pollution On Crop Productivity In China

Tropospheric ozone is one of main species in photochemical smog.Currently,it has become one of the most important air pollutants in China and the focus of government and public attention.The increasing emissions of Ozone precursors NOx and VOCs as a result of the rapid development of economy has dramatically promoted ozone concentration in decades.Due to its strong oxidizing,ozone could damage not merely human health but also vegetation through stomatal on the surface of leaves into tissue.As a major agricultural country,ozone stress will lead to decreasing crop yields,which may bring about food security problems.This research is divided into two parts.The first part is focused on the ozone and winter wheat in Yangtze River Delta(YRD).We use hourly ozone observation data released by the National Environmental Monitoring Station to analyze the temporal and spatial distribution characteristics of ozone pollution and to calculate M7(Mean daytime 7 h ozone concentration between 09:00 and 16:00)index and AOT40(Accumulated exposure over a threshold ozone concentration of 40 ppb)index.We then use ozone dose-winter yield response model to calculate relative yield loss(RYL)and crop production loss(CPL)of each county in YRD,then evaluate the impact of ozone on the yield of winter wheat in YRD.In the second part,the influence of ozone stress on crop productivity is studied by using ozone flux-response model in China.Firstly,the air quality model WRF-CMAQ is used to simulate ozone concentration in China in 2014.Based on the simulated ozone concentration,temporal and spatial characteristics of ozone distribution are descripted.Then,based on the existing ozone flux empirical model,the ozone flux effect module is added to the BEPS model to simulate the gross primary productivity(GPP)of crops in China in 2014 to comprehend the impact of ozone to crop productivity.The main results are as follows:(1)Ozone concentration increases gradually by time in the YRD in spring,and the north is higher than the south.Concentration in Lianyungang and other places of northern Jiangsu province are the highest,southwest mountain area of Zhejiang province are the lowest,Shanghai,southern Jiangsu province and northern Zhejiang province are between them.The ozone concentration in spring,especially in May,are exceeding the China's national standards seriously.In half of the YRD cites,there are more than 10 days exceeding the standard,in which Nanjing and Yangzhou have the maximum exceeding standard days,with values of 27 and 20 days,respectively.(2)Ozone pollution in the YRD region can lead to the region's average winter wheat RYL of 5.7%(M7)to 25.5%(AOT40)and CPL of 7.85×105t(M7)to 4.49×1 06 t(AOT40).The most serious occurs in northern Jiangsu,where RYL is about 5.8%to 25.9%and CPL is about 6.77×105 t(M7)to 3.86×106t(AOT40)in this area.(3)In 2014,the average daily ozone concentration in summer in China is the highest,followed by spring,autumn and winter.In the summer,ozone concentration is highest in the eastern region with average concentration higher than 70 ppb,while in other seasons,the western region is higher.In spring,concentration of ozone in Chengdu and Chongqing are higher than 60 ppb,Fujian,Jiangxi,Hunan,Guizhou,Hubei and other regions are more than 50 ppb.In winter,the average ozone concentration in the eastern part of China is below 30 ppb.(4)In 2014,China's crop GPP appears highest in eastern Henan and northern Anhui.The GPP of the crops in the North China Plain,the middle-lower Yangtze Plain,the Sichuan Basin and the Northeast Plain are higher,and in the northwest and southern China are lower.The total GPP of the crops is 1.70 Pg C yr-1.GPP in low and high ozone sensitivity scenario is 1.43 Pg C yr-1 and 1.39 Pg C yr-1,respectively,with an average decrease of 15.8%and 18.2%,respectively.In both sensitivity scenario,the impact of ozone on crop GPP is more than 10%in most parts of eastern China.(5)Based on ozone flux approach,crop GPP loss is 18%under low ozone sensitivity scenario and 20%under high ozone sensitivity scenario in YRD,respectively.The results are between RYL of M7 index and RYL of AOT40 index.Although the flux model is computationally complex and the model itself is deficient,it proves that the results of the flux method are more reliable.